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Robert[_3_]

On 2009-09-09 15:20:42 +0100, said:

On Wed, 09 Sep 2009 14:41:14 +0100
Bruce wrote:
On Wed, 9 Sep 2009 12:38:35 +0000 (UTC), wrote:

Really, whys that then? Would the actual boring part of the TBM cost
substantially more if its diameter was increased by a metre? Would the extra
concrete cost raise the project costs much higher? Or are you just BSing
because you always want to appear to know best?

This is an area where I have specialist knowledge, both as someone who
has worked on several tunnelling projects and someone who has been
responsible for tendering for tunnelling projects.

For the record, I don't believe you.

The cost of the tunnelling machine increases quite dramatically with
tunnel diameter; the cost of the excavation and of the tunnel lining
increases approximately with the square of the excavated diameter.

*sigh* I hate to break this pre-GCSE news to you, but the area of the
shaft of a cylinder increases *linearly* with increasing radius, not as the
square of it so the cost of the lining will not go up like that. The formula
you want incidentaly is 2*pi*r*h. So before you post anymore bull****
pretending your in-the-biz you might want to revisit your school books first.
As for the cost of the TBM - an extra metre diamater of the boring plate
would make no difference to the machinary required behind it.

B2003

But the volume of material being excavated /does/ increase as the
square of the diameter. If the tunnel diameter is increased from 6.5
metres to 7.5 metres, a 15 per cent increase, the volume of spoil
increases by 33 per cent. (All numbers rounded).

This is not insignificant. The machinery driving the 'boring plate'
would have to be scaled up to cope and the extra spoil disposed of.
--
Robert